<meta charset="utf-8">
(#) Missing Documentation Example

!!! WARNING: Missing Documentation Example
   This is a warning.

Id
:   `LintDocExample`
Summary
:   Missing Documentation Example
Note
:   **This issue is disabled by default**; use `--enable LintDocExample`
Severity
:   Warning
Category
:   Lint Implementation Issues
Platform
:   JDK
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   7.0.0 (July 2021)
Affects
:   Kotlin and Java files and test sources
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/LintDetectorDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/LintDetectorDetectorTest.kt)

Lint's tool for generating documentation for each issue has special
support for including a code example which shows how to trigger the
report. It will pick the first unit test it can find and pick out the
source file referenced from the error message, but you can instead
designate a unit test to be the documentation example, and in that case,
all the files are included.

To designate a unit test as the documentation example for an issue, name
the test `testDocumentationExample`, or if your detector reports
multiple issues, `testDocumentationExample`<Id>, such as
`testDocumentationExampleMyId`.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/MyKotlinLintDetectorTest.kt:10:Warning: Expected to also
find a documentation example test (testDocumentationExample) which shows
a simple, typical scenario which triggers the test, and which will be
extracted into lint's per-issue documentation pages [LintDocExample]
    fun testBasic() {
    ^
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`src/test/pkg/MyJavaLintDetector.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
/* Copyright (C) 2020 The Android Open Source Project */
package test.pkg;
import com.intellij.psi.PsiClass;
import com.intellij.psi.PsiCallExpression;
import com.intellij.psi.PsiExpression;
import com.intellij.psi.PsiField;
import com.intellij.psi.PsiMethod;
import com.intellij.psi.util.PsiTreeUtil;
import com.android.tools.lint.detector.api.Detector;
import org.jetbrains.uast.UFile;
import org.jetbrains.uast.UMethod;
import org.jetbrains.uast.UField;
import com.android.tools.lint.detector.api.Category;
import com.android.tools.lint.detector.api.Detector;
import com.android.tools.lint.detector.api.Implementation;
import com.android.tools.lint.detector.api.Issue;
import com.android.tools.lint.detector.api.JavaContext;
import com.android.tools.lint.detector.api.Scope;
import com.android.tools.lint.detector.api.Severity;
import org.jetbrains.uast.UCallExpression;
import java.util.EnumSet;

@SuppressWarnings({"MethodMayBeStatic", "ClassNameDiffersFromFileName", "StatementWithEmptyBody", "deprecation"})
public class MyJavaLintDetector extends Detector {
    public static final Issue ISSUE =
            Issue.create(
                    "com.android.namespaced.lint.check.FooDetector",
                    "Wrong use of <LinearLayout>",
                    "As described in "
                        + "https://code.google.com/p/android/issues/detail?id=65351 blah blah blah.",
                    Category.A11Y,
                    3,
                    Severity.WARNING,
                    new Implementation(MyJavaLintDetector.class, EnumSet.of(Scope.RESOURCE_FILE, Scope.JAVA_FILE)))
                    .addMoreInfo("file://explanation.doc")
                    .addMoreInfo("http://my.personal.blogger.com/aboutme.htm")
                    .addMoreInfo("mailto:lint@example.com");
    public void testGetBody(PsiMethod method) {
        method.getBody(); // ERROR - must use UAST
    }
    public void testGetBody(UMethod method) {
        method.getBody(); // ERROR - must use UAST
    }
    public void testGetContainingClass(UMethod method, UField field) {
        method.getContainingClass(); // ERROR - must use UAST
        field.getContainingClass(); // ERROR - must use UAST
    }
    public void testGetContainingClass(PsiMethod method, PsiField field) {
        method.getContainingClass(); // OK - legitimate uses after resolve
        field.getContainingClass(); // OK - legitimate uses after resolve
    }
    public void testEquals(PsiCallExpression element1, PsiExpression element2) {
        if (element1.equals(element2)) { }
        if (element2.equals(element1)) { }
        if (element1 == element2) { }
        if (element1 != element2) { }
    }
    public void testGetInitializer(PsiField field) {
        field.getInitializer(); // ERROR - must use UAST
    }
    public void testParents(PsiField field, UMethod method) {
        PsiElement parent = field.getParent(); // OK
        PsiElement parent = method.getParent(); // ERROR
        PsiTreeUtil.getParentOfType(field, PsiClass.class); // OK
        PsiTreeUtil.getParentOfType(method, PsiClass.class); // ERROR
    }

    public void testReport(JavaContext context, UCallExpression node) {
        context.report(ISSUE, node, context.getLocation(node),
            "Wrong use of LinearLayout.");
        context.report(ISSUE, node, context.getLocation(node),
            "First problem. Second problem.");
        context.report(ISSUE, node, context.getLocation(node),
            "This is teh typo");
        String message = "Welcome to Andriod";
        context.report(ISSUE, node, context.getLocation(node), message);
        context.report(ISSUE, node, context.getLocation(node),
            "Should you use `x ?: y` instead of ```foo ? 1 : 0``` ?");
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/MyKotlinLintDetector.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
/* Copyright (C) 2020 The Android Open Source Project */
package test.pkg
import com.intellij.psi.PsiCallExpression
import com.intellij.psi.PsiExpression
import com.intellij.psi.PsiField
import com.intellij.psi.PsiMethod
import com.intellij.psi.util.PsiTreeUtil
import com.android.tools.lint.detector.api.Category
import com.android.tools.lint.detector.api.Detector
import com.android.tools.lint.detector.api.Implementation
import com.android.tools.lint.detector.api.Issue
import com.android.tools.lint.detector.api.JavaContext
import com.android.tools.lint.detector.api.Scope
import com.android.tools.lint.detector.api.Severity
import org.jetbrains.uast.UCallExpression

class MyKotlinLintDetector : Detector() {
    fun testGetBody(method: PsiMethod) {
        val body = method.body // ERROR - must use UAST
    }
    @Suppress("ReplaceCallWithBinaryOperator","ControlFlowWithEmptyBody")
    fun testEquals(element1: PsiCallExpression, element2: PsiExpression) {
        if (element1.equals(element2)) { }
        if (element2.equals(element1)) { }
        if (element1 == element2) { }
        if (element1 === element2) { }
        if (element1 != element2) { }
        if (element1 !== element2) { }
        if (element1 == null) { } // OK
        if (element1 === null) { } // OK
        if (element1 != null) { } // OK
        if (element1 !== null) { } // OK
    }
    @Suppress("UsePropertyAccessSyntax")
    fun testGetInitializer(field: PsiField) {
        field.getInitializer() // ERROR - must use UAST
        field.initializer // ERROR - must use UAST
    }
    fun testParents(field: PsiField) {
        val parent = field.parent
        val method = PsiTreeUtil.getParentOfType(field, PsiMethod::class.java)
    }

    fun testReport(context: JavaContext, node: UCallExpression) {
        context.report(ISSUE, node, context.getLocation(node),
             """
                    |Instead you should call foo().bar().baz() here.
                    |""".trimIndent())
    }

    companion object {
        private val IMPLEMENTATION =
            Implementation(
                MyKotlinLintDetector::class.java,
                Scope.JAVA_FILE_SCOPE
            )

        val ISSUE =
            Issue.create(
                id = "badlyCapitalized id",
                briefDescription = "checks MyLintDetector.",
                explanation = """
                    Some description here.
                    Here's a call: foo.bar.baz(args).
                    This line continuation is okay. \
                    But this one is missing a space.\
                    Okay?
                    """.trimIndent(),
                category = Category.INTEROPERABILITY_KOTLIN,
                moreInfo = "https://code.google.com/p/android/issues/detail?id=65351", // OBSOLETE
                priority = 4,
                severity = Severity.WARNING,
                implementation = IMPLEMENTATION
            )
            .addMoreInfo("https://issuetracker.google.com/issues/3733548") // ERROR - missing digit
            .addMoreInfo("https://issuetracker.google.com/issues/373354878") // OK - including digit
            .addMoreInfo("http://issuetracker.google.com/issues/37335487") // ERROR - http instead of https
            .addMoreInfo("https://b.corp.google.com/issues/139153781") // ERROR - don't point to buganizer with internal link
            .addMoreInfo("https://goo.gle/policy-storage-help") // OK - regression test for goo.gle
    }

    override fun visitAnnotationUsage(
        context: JavaContext,
        element: org.jetbrains.uast.UElement.UElement,
        annotationInfo: com.android.tools.lint.detector.api.AnnotationInfo,
        usageInfo: com.android.tools.lint.detector.api.AnnotationUsageInfo
    ) {
        // Invalid recursion!
        super.visitAnnotationUsage(context, element, annotationInfo, usageInfo)
    }

    fun misc() {
        System.out.print("Debugging")
        println("Debugging code")
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/MyIssueRegistry.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package test.pkg
import com.android.tools.lint.client.api.IssueRegistry
class MyIssueRegistry : IssueRegistry() {
    override val issues = listOf(
        MyJavaLintDetector.ISSUE,
        MyKotlinLintDetector.Companion.ISSUE
    )
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/MyVendorIssueRegistry.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package test.pkg
import com.android.tools.lint.client.api.IssueRegistry
import com.android.tools.lint.client.api.Vendor
class MyVendorIssueRegistry : IssueRegistry() {
    // Supplies a vendor: no warning
    override var vendor: Vendor? = Vendor("Unit test")
    override val issues = listOf(
        MyJavaLintDetector.ISSUE,
        MyKotlinLintDetector.Companion.ISSUE
    )
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/InheritingRegistry.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package test.pkg
import com.android.tools.lint.client.api.IssueRegistry
import com.android.tools.lint.client.api.Vendor
class InheritingRegistry : MyVendorIssueRegistry() { // NO WARNING
    // This registry doesn't supply a vendor but inherits one; no warning
    override val issues = listOf(
        MyJavaLintDetector.ISSUE,
        MyKotlinLintDetector.Companion.ISSUE
    )
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/MyKotlinLintDetectorTest.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
// Copyright (C) 2021 The Android Open Source Project
package test.pkg
import com.android.tools.lint.checks.infrastructure.LintDetectorTest
import com.android.tools.lint.detector.api.Detector
class MyKotlinLintDetectorTest : LintDetectorTest() {
    override fun getDetector(): Detector {
        return MyKotlinLintDetector()
    }

    fun testBasic() {
        val expected = """
            src/test/pkg/AlarmTest.java:9: Warning: Value will be forced up to 5000 as of Android 5.1; don't rely on this to be exact [ShortAlarm]
                    alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME, 50, 10, null); // ERROR
                                                                             ~~
            0 errors, 1 warnings
            """

        lint().files(
            kotlin(
                """
                fun test() {
                    println("Value=${"$"}")
                }
                """
            ),
            java(
                "src/test/pkg/AlarmTest.java",
                """
                    package test.pkg;

                    import android.app.AlarmManager;
                    @SuppressWarnings("ClassNameDiffersFromFileName")
                    public class AlarmTest {
                        public void test(AlarmManager alarmManager) {
                            alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME, 5000, 60000, null); // OK
                            alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME, 6000, 70000, null); // OK
                            alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME, 50, 10, null); // ERROR
                            alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME, 5000,  // ERROR
                                    OtherClass.MY_INTERVAL, null);                          // ERROR
                        }

                        private static class OtherClass {
                            public static final long MY_INTERVAL = 1000L;
                        }
                    }
                    """.trimIndent()
            )
        ).run().expect(expected)
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/LintDetectorDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `LintDetectorDetector.testProblems`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("LintDocExample")
  fun method() {
     expect(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("LintDocExample")
  void method() {
     expect(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection LintDocExample
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="LintDocExample" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'LintDocExample'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore LintDocExample ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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